Technical Field
Examples disclosed herein relate generally to the detection of cardiac function in a patient, and more particularly to the detection of cardiac function and the treatment of cardiac conditions in an ambulatory medical device, such as a wearable defibrillator.
Discussion
With a wearable defibrillator worn by an ambulatory patient, the patient's electrocardiogram (ECG) signal is obtained from body surface electrodes. Determining the true characteristics of an ambulatory patient's cardiac cycle based on an ECG signal in this manner can be difficult. Electrical noise and electrode fall-off frequently degrade the quality of the ECG signal. In addition, the characteristics of ECG signals vary from patient to patient due to factors such as the patient's state of health, individual physiology, and electrode positions on the body surface.
Known ambulatory wearable defibrillators, such as the LifeVest® Wearable Cardioverter Defibrillator available from Zoll Medical Corporation of Chelmsford, Mass., use four ECG sensing electrodes in a dual-channel configuration. That is, an electrical signal provided by one of the four ECG sensing electrodes is paired with the electrical signal provided by another of the four ECG sensing electrodes to form a channel. This arrangement of ECG sensing electrodes is usually suitable because in most cases it is rare that noise or electrode movement affects the entire body circumference. The dual-channel configuration provides redundancy and allows the system to operate on a single channel if necessary. Because signal quality also varies from patient to patient, having two channels provides the opportunity to have improved signal pickup, since the ECG sensing electrodes are located in different body positions.